1. Field of the Invention
This invention relates to an improved process for converting coal or similar solid carbonaceous materials. More particularly, this invention relates to an improved process for liquefying coal and similar carbonaceous substances.
2. Description of the Prior Art
As is well known, coal has long been used as a fuel in many areas. For several reasons, such as handling problems, waste disposal problems, pollution problems and the like, coal has not been a particularly desirable fuel from the ultimate consumers point of view. As a result, oil and gas have enjoyed a dominant position, from the standpoint of fuel sources, throughout the world.
As is also well known, proven petroleum and gas reserves are shrinking throughout the world and the need for alternate sources of energy is becoming more and more apparent. One such alternate source is, of course, coal since coal is an abundant fossil fuel in many countries throughout the world. Before coal will be widely accepted as a fuel, however, it is believed necessary to convert the same to a form which will not suffer from the several disadvantages alluded to previously.
To this end, several processes wherein coal is either liquefied and/or gasified have been proposed heretofore. Of these, the processes wherein coal is liquefied appear to be more desirable since a broader range of products is produced and these products are more readily heretofore. Of these, the processes wherein coal is liquefied appear to be more desirable since a broader range of products is produced and these products are more readily transported and stored.
Of these several liquefaction processes which have been heretofore proposed, those processes wherein coal is liquefied in the presence of a solvent or diluent, particularly a hydrogen-donor solvent or diluent, and a hydrogen containing gas appear to offer the greater advantages. In these processes, liquefaction is accomplished at elevated temperatures and pressures and hydrocarbon gases are invariably produced as byproducts. Moreover, none of the prior art processes have resulted in complete conversion of the coal or similar solid carbonaceous materials. As a result, a normally solid residue containing ash and unconverted coal is also invariably obtained. The gaseous products and/or the residue can be further processed to provide process hydrogen or can be burned to produce process energy. The quantity of gaseous products and unconverted coal, however, generally exceeds the quantity required for an overall energy and hydrogen balance. Moreover, the cost of recovering hydrogen and/or the heating value of the unconverted coal remaining in the residue is generally excessive. The need, therefore, for a liquefaction process which will maximize coal conversion thereby minimizing unconverted coal in the residue, is believed to be readily apparent. Moreover, the need for such a liquefaction process resulting in reduced gas yields is also believed to be apparent.